An automated refractor, or “autorefractor,” is a computer-controlled machine used during an eye examination to provide an objective measurement of a person's refractive error and prescription (“Rx”) for glasses or contact lenses. This is achieved by measuring how light is changed as it enters a person's eye. Autorefractors are commercially-available from Unicos USA LLC (Miami, Fla.), Topcon (Oakland, N.J.), Tomey (Phoenix, Ariz.), and Carl Zeiss Vision, Inc. (San Diego, Calif.), for example.
Wavefront sensors (also known as “wavefront aberrometers”) are a type of instrument that measure wavefront errors of a person's eye (e.g., second and higher order Zernike coefficients). A variety of techniques exist for determining an Rx from the wavefront errors. In some approaches, model-based techniques are used. Such techniques can use optical simulation software (e.g., ray-tracing software) to establish a second-order (e.g., power and astigmatism) correction suitable for the measured eye based on the measured wavefront errors. In many cases, the Rx calculated from the wavefront errors is not the same as an Rx determined for a person using a subjective refraction. Examples of commercially-available wavefront sensors include the i.Profilerplus®, from Carl Zeiss Vision, Inc.
A common use for an autorefractor is to give an optometrist starting values for the sphere, cyl, and axis (or, correspondingly, M, J0, and J45) for performing a subjective refraction. The final Rx for that person is then determined using the subjective refraction. In general, the closer the starting values are to the final prescription, the less time the optometrist spends in finding the final Rx.